Abstract
To determine quantitative SI joint MRI lesion cut-offs that optimally define a positive MRI for inflammatory and structural lesions typical of axial SpA (axSpA) and that predict clinical diagnosis. The Assessment of SpondyloArthritis international Society (ASAS) MRI group assessed MRIs from the ASAS Classification Cohort in two reading exercises where (A) 169 cases and 7 central readers; (B) 107 cases and 8 central readers. We calculated sensitivity/specificity for the number of SI joint quadrants or slices with bone marrow oedema (BME), erosion, fat lesion, where a majority of central readers had high confidence there was a definite active or structural lesion. Cut-offs with ≥95% specificity were analysed for their predictive utility for follow-up rheumatologist diagnosis of axSpA by calculating positive/negative predictive values (PPVs/NPVs) and selecting cut-offs with PPV ≥ 95%. Active or structural lesions typical of axSpA on MRI had PPVs ≥ 95% for clinical diagnosis of axSpA. Cut-offs that best reflected a definite active lesion typical of axSpA were either ≥4 SI joint quadrants with BME at any location or at the same location in ≥3 consecutive slices. For definite structural lesion, the optimal cut-offs were any one of ≥3 SI joint quadrants with erosion or ≥5 with fat lesions, erosion at the same location for ≥2 consecutive slices, fat lesions at the same location for ≥3 consecutive slices, or presence of a deep (i.e. >1 cm depth) fat lesion. We propose cut-offs for definite active and structural lesions typical of axSpA that have high PPVs for a long-term clinical diagnosis of axSpA for application in disease classification and clinical research.
Highlights
Magnetic resonance imaging (MRI) of the sacroiliac joints (SIJ) represents a major advance in the evaluation of axial spondyloarthritis because it permits detection of inflammatory and structural changes in the subchondral bone marrow that are not visible on conventional radiography of the SIJ [1]
Structural lesions typical of axial spondyloarthritis (axSpA) were observed on baseline MRI scans by a majority of readers (≥4/7) in 32.4% and 36.5% of cases diagnosed with axSpA at baseline and follow up, respectively, as compared to 6.8% and 0% diagnosed as non-axSpA (Table 1)
ASASdefined bone marrow edema (BME) in ≥4 SIJ quadrants at any location or in the same location on ≥3 consecutive slices were optimal for defining a definite active lesion typical of axSpA
Summary
Magnetic resonance imaging (MRI) of the sacroiliac joints (SIJ) represents a major advance in the evaluation of axial spondyloarthritis (axSpA) because it permits detection of inflammatory and structural changes in the subchondral bone marrow that are not visible on conventional radiography of the SIJ [1]. A positive MRI indicative of sacroiliitis was first defined in 2009 according to a consensus opinion of ASAS experts in MRI as the presence of subchondral bone marrow edema (BME) that is “highly suggestive” of axSpA on STIR/fat-suppressed T2 (T2FS) or osteitis on contrastenhanced fat-suppressed T1 (T1FS+Gd) MRI [8]. This ASAS definition included a quantitative component, this being the presence of two BME lesions on a single semicoronal slice through the SIJ or a single lesion on two consecutive semicoronal slices. This is a potential concern because definitions intended for classification purposes may be misused for diagnosis
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